The present invention generally relates to production of optical modules and more particularly to the art of coupling a light emitting device or a photoreception device in an optical module to an optical fiber.
Optical networks support transmission of very large amounts of information with very high speed and is expected to play a major role in the near future particularly in relation to so-called multi-media applications in which image data including motion picture data and audio data are treated as a part of the information to be processed. In order that the human society accepts such multi-media as a part of the culture, it is necessary to provide the optical network as well as information processing terminals connected thereto at a cost as low as possible.
In order to connect various information processing terminals to the optical network, a so-called optical module is used, in which a photoreception device such as photodiode and a light emitting device such as laser diode are integrated. In such optical modules, it has been necessary to carry out a complex adjustment for achieving an optimum optical coupling between the photoreception device or the light emitting device in the module and the optical fiber.
For example, it is necessary to assemble an optical module with such precision that the optical beam emitted from a laser diode, provided in the optical module as a light emitting device, is focused, by a lens at a point located within 0.1 .mu.m from the edge surface of a corresponding optical fiber. Conventionally, such an adjustment of the laser diode with respect to the optical beam edge has been achieved by observing the intensity of the optical beam in the optical fiber while continuously driving the laser diode during such an adjustment process.
FIG. 1 shows the constitution of an assembling rig used conventionally for producing an optical module assembly.
Referring to FIG. 1, an optical module includes a case 1a that holds a lens 3 and a laser diode 2, wherein it will be noted that a cylindrical body of the laser diode is fitted into the lens case 1a. After the laser diode 2 is thus mounted upon the case 1a, the relationship between the laser diode 2 and the lens 3 is fixed. Further, a fiber holder 6 that holds an end of an optical fiber 4 via a ferrule 5 is abutted to the case 1a. The ferrule 5 protects the end part of the optical fiber 4 as usual.
When fixing the fiber holder 6 upon the lens case 1a, a triaxial stage 7 is used. More specifically, the fiber holder 6 is held on the triaxial stage 7 in the state that the fiber holder 6 holds the optical fiber 4 as indicated, and the position of the triaxial stage 7 is adjusted for each of three axes x, y and z, while observing the optical beam at the other end of the optical fiber, so that the optical beam intensity in the optical fiber 6 becomes maximum.
However, such a conventional assembling process of the optical module has a drawback in that it takes about 30 seconds for conducting the adjustment for each of the foregoing x, y and z axes. This means that it takes about 1 minute and 30 seconds for adjustment of all three axes.
The reason such a long time is needed for the adjustment is that: (1) a stringent accuracy of 0.1 .mu.m or less is required between the optical fiber edge and the optical module in order to achieve the necessary optical coupling; (2) it is necessary to direct the output beam of the laser diode into the core of the optical fiber before starting any adjustment at all, while the optical fiber core has a diameter of only about 9 .mu.m; no adjustment is possible at all unless the optical beam of the laser diode hits the optical fiber core; (3) the output beam of the laser diode is an infrared beam, thus making it difficult to carry out a coarse adjustment by visual operation; (4) the optical components generally have substantial variation in the dimension due to poor precision of fabrication, leading to a substantial variation in the optimum position (as much as 500 .mu.m), and the like.